1. Field of the Invention
This invention relates to a method for degumming decorticated plant bast fiber to remove pectin-containing material therefrom and, more particularly, to a method for degumming decorticated ramie bast fiber.
2. Description of the Prior Art
Most of the major plant fibers of the world can be characterized either as stem, or bast, fibers or can be characterized as leaf fibers. This invention is primarily concerned with degumming decorticated bast fibers, such as ramie or hemp, to remove the pectin-containing material that surrounds the individual bast fibers.
A bark-like covering surrounds the bast fibers and the pectin-containing material around each fiber to form an outer sheath. The breaking down and/or removing of a substantial portion of this outer sheath is generally referred to as decortication. Decortication can be accomplished manually or by known conventional mechanical decorticating apparatus.
A substantial proportion of the pectin-containing material which surrounds the individual bast fibers is pectin, with the remaining portion being primarily various water soluble constituents. Pectin is a polymer similar in chemical structure and behavior to cellulose. Pectin is generally insoluble in water or acid, but may be broken down in an alkaline solution, such as an aqueous solution of sodium hydroxide.
Removal of the pectin-containing material, or gum, is necessary, in many instances, for utilization of the fiber for its intended purposes. Various methods are known which encompass degumming, or removing, the pectin-containing substances from the individual bast fiber. For example, U.S. Pat. No. 2,407,227 to Earle discloses a retting method for the treatment of fibrous vegetable or plant material, such as flax, ramie, and hemp.
Retting is defined in the Earle patent as the facilitation of the separation of the individual fibers from the surrounding plant matter and from each other, through the breaking down, or removal from the plant structure, by means of fermentation, of the waxy, resinous, or gummy binding substances present in the plant.
Earle discloses a method for the retting of flax and analogous fibers in plant material, as mentioned above, which is carried out in an enzymically-active solution having a mildly acidic pH. Earle's method consists of positively acidifying water to a degree approaching and slightly less than the optimum acid concentration for enzymatic activity. To this solution there is added an amount of enzymically-active solution from a previous ret so as to bring the concentration of acid of the resulting mixture to the optimum value. The mixture is then heated to a temperature which will maximize enzymatic action. The flax or other analogous fibrous plant material is then steeped into the mixture which is maintained at a sustained elevated temperature. The fibrous plant material is removed from the mixture when the acid concentration of the solution in which the fibrous plant material is steeped begins to decline.
Earle mentions that if decorticated fiber is to be retted, the water can be more highly acidified, even to a pH of 4.0, then heated preferably to a temperature of 90.degree. F. to 95.degree. F. and then mixed with a suitable amount of heated solution from a previous ret. If solution from a previous ret is not available, the solution may be developed through the retting of detached shives, for example. In Earle, it is mentioned that retting of decorticated material requires a total time of not more than 24 to 36 hours.
U.S. Pat. No. 2,871,163 to Turnbull discloses a method for the separation of fiber from fiber-containing plants such as jute, kenaf, ramie, flax, sisal, abaca, and hemp. In Turnbull, a cytase-containing liquor is extracted from plants of the same kind as those for which fiber separation is to be accomplished. The fiber-containing plant portions are crushed, and the crushed portions are treated for a period of one to four days at a temperature between 30.degree. C. and 60.degree. C. with the cytase-containing liquor to decompose the pectin or pectinaceous compounds of the plants to free the fibers therefrom. Examples of cytases given in Turnbull are pectases, pectinase, and protopectinase. Turnbull mentions that the cytases may also be found in certain fruits, vegetables, various fungi and bacteria; and cytases obtained from these sources may be used in Turnbull's method. Turnbull states that it is advantageous to maintain the pH of the extracted cytase-containing liquor at between 6 and 8, and preferably below 7.
U.S. Pat. No. 2,725,289 to Lourd discloses a process for the chemical retting or ramie, flax, hemp, jute, and the like. In the process of the Lourd patent, the fibrous material is subjected to a first treatment by an aqueous solution having an alkali base containing a palmitate of an amine base which functions as an emulsifier; and then to a second treatment with an aqueous solution which includes the same substances as that in the first treatment and additionally contains an oxidizing agent.
U.S. Pat. No. 1,941,793 to Faut discloses a retting process of textile materials. In Faut, a special compound is added to the retting water. The special compound is composed of saponified fatty stuffs to which are added, in certain proportions, salts from strong bases and weak acid. These saponified fatty substances divide and dissolve in the retting water providing a coating to protect the fibers from the action of the free nascent alkali liberated in the incompletely saturated medium.
U.S. Pat. No. 1,842,024 to Hollander et al. discloses a process for retting fibers in which a cellulose fiber is surrounded by a cortex of ligneous material, such as flax, ramie, jute, sisal, hemp, etc. In Hollander's method, an enzyme capable of digesting a cortex of ligneous material surrounding a cellulose fiber is added to the retting bath. Hollander mentions that suitable enzymes include enzymes prepared from fungi, such as species of Aspergillus. The Hollander patent mentions that best results are obtained in a bath having a pH value of from 5 to 8 with an optimum pH value being about 7. The patent further mentions that the pH value of the enzyme bath is regulated by the addition of acids, such as acetic acid and sulfuric acid. This patent mentions that the duration of the enzyme step can vary, but generally will be between 24 and 48 hours.
In the process of the Hollander et al. patent, the fibers are first subjected to an alkaline bath and are then subjected to the enzyme bath. The chemical alkaline bath serves to open the cortex of ligneous material to make the cortex more accessible to the action of the enzyme bath. Hollander et al. states that a buffer is preferably added to the chemical alkaline bath to protect the cellulose fibers from the action of the alkaline liquid.
U.S. Pat. No. 1,795,528 to Watson et al. discloses a process of producing fiber and yarn from flax. In the process, the fibers are eventually twisted into a rove. The rove is wound onto an open reel and retted bacteriologically to soften the gummy matter associated with the fibers.
U.S. Pat. No. 1,746,316 to Marcus discloses a process for retting textile fibers, such as flax, jute, and ramie. In the method of the Marcus patent, a nitrogen fixing bacteria is added to the retting process to degum the gum or pectin from the fiber.
U.S. Pat. No. 1,133,590 to Toles discloses a method and apparatus for retting fibrous materials. In this patent, a specific ferment is added to the retting fluid and acts as a natural solvent of the gummy substances and hastens the removal of the gummy substances from the fiber. This ferment is a specific pectin ferment which hastens the propagation of the retting bacteria.
U.S. Pat. No. 103,275 to Allen discloses a process for loosening or separating long-line fiber, such as ramie fiber, from its hard woody stalk by means of a fermenting bath.
U.S. Pat. No. 1,017,176 to Schreckenbach discloses a method of treating raw and worked textile fibers, such as jute, hemp, and ramie. In this patent, glycerin is added to a fermenting bath to promote the growth of an effective organized ferment. The organized ferment has the effect of dissolving the gummy material in the fibers and loosening the bundles of cells. The core of the cell, however, is left intact.
In an article entitled "A Method of Degumming and Bleaching Ramie Fibers and Their Physical Properties" by Venkateswaran appearing in "Tappi", Volume 48, no. 3, (March, 1965), two procedures for degumming ramie fibers are disclosed. The first procedure includes an ethyl alcohol extraction of the fiber for a 2 to 4 hour period and a treatment of the fiber for a period of two hours with a boiling sodium hydroxide solution. In the second procedure, the ramie fibers were soaked in ethanol overnight; and the ethanol-treated fibers were washed with deionized water.
In an article entitled "Cultivation of Ramie in West Bengal, India" by Nandi et al., Soil and Crop Science Society of Florida, Proceedings, Volume 24, pp. 418-425, (1964), it is disclosed that degumming of ramie fiber is accomplished by alkali treatments by boiling in large open pans and can also be carried on by microbiological retting.
In the article "Progress Report on the Chemical Degumming of Ramie by an In-line, Open-cook Process" by Allison et al., Soil and Crop Science Society of Florida, Proceedings, Volume 22, pp. 176-185 (1962), an in-line degumming apparatus for degumming ramie fiber by moving the fiber through the apparatus through a degumming solution is disclosed. The contents of the degumming solution are apparently not disclosed in this article; and the article mentions that such in-line apparatus can accomplish the degumming in from about 7 to 10 minutes. However, this article notes that the denier, or the weight, in grams, of a fiber 9,000 meters in length, is consistently higher when compared with conventionally known pressure degumming systems by a factor as much as 1.5 to 2.0 units or more. The article indicates that the higher denier suggests something is remaining in the fiber degummed by such in-line apparatus. The article concludes that the actual usefulness of ramie fiber coming from the in-line method of degumming was still, at the time of the writing of the article, to be proven at the industrial level.
As can be seen from the foregoing, conventionally known processes for degumming plant bast fiber, such as ramie and hemp, require a considerable amount of time, may degrade the fiber, or may leave various impurities with the fiber which may not be desirable in certain applications or uses for the fiber.
What is needed, therefore, is a method for degumming plant bast fiber, such as ramie or hemp bast fiber, which can accomplish degumming of the fiber in a substantially short period of time, and provide a high quality product that is at least equal to or superior to that obtainable by conventional degumming methods.